Maruse Sadek

Stereochemical course of glucan hydrolysis by barley (1 → 3)- and (1 → 3,1 → 4)-β-glucanases

The stereochemical course of hydrolysis of Laminaria digitata laminarin and barley (1-->3, 1-->4)-beta-glucan by barley (1-->3)-beta-glucanase (E.C. 3.2.1.39) isoenzyme GII and (1-->3, 1-->4)-beta-glucanase (EC 3.2.1.73) isoenzyme EII, respectively, has been determined by 1H-NMR. Both enzymes catalyse hydrolysis with retention of anomeric configuration (e-->e) and may therefore operate via a double displacement mechanism. We predict that all other members of Family 17 of beta-glycosyl hydrolases also follow this stereochemical course of hydrolysis.

Synthesis and phototoxicity of a series of haematoporphyrin analogues

Abstract The synthesis of new haematoporphyrin analogues is described. These porphyrins have been assayed for phototoxicity and cellular localization and show promise for use in photodynaic therapy of cancer.

The hybridization state of nitrogen as a conformational variable in biologically active molecules

A survey of the conformations found in the crystal structures of central nervous system-active drugs and related nitrogen-containing structures shows that there is a continuous distribution of conformations from that typical of the sp3(N-torsion 120°) to that typical of the sp2(N-torsion 180°) hybridization state. In general the presence of an adjacent carbonyl group favours a planar geometry, while the lack of any conjugating group favours the tetrahedral state, but nitrogens with aromatic substituents cover the entire range between the two states. Other than those cases where the nitrogen has aromatic substituents or is in a sterically constrained ring-system (e.g., cage compounds), steric effects have relatively little influence on the conformation at nitrogen. In these cases calculations using various techniques suggest that simple non-bonded potential calculations may be the most practical approach to the evaluation of nitrogen geometry. Even in small molecules, however, calculated barriers to nitrogen inversion are generally low and poorly reproduced by either molecular orbital or classical calculations.

Novel products from attempted michael addition to 1-methyl-1,2,5,6-tetrahydropyridine-4-carbonitrile

Abstract The reaction of some phenols with the title compound, in the presence of sodium, gives 2-(2-hydroxyaryl_piperidine derivatives. Geometrical isomers have been separated, which differ in having an equatorial (A) or axial (B) cyano group on the piperidine chair (the methyl and aryl groups are equatorial in both forms). The x-ray crystallographic structures of an example of each of A and B are reported and the proton NMR spectra are assigned.

The detection and quantification of apiose by capillary gas chromatography of its alditol acetates

The branched-chain sugar, apiose [3-C-(hydroxymethyl)-D-glycero-aldotetrose] occurs widely in plants, in low molecular weight glycosides’, and as a component of cell-wall polysaccharides’-s. Problems have been encountered in the analysis of apiose as its alditol acetate derivatives. For example, when pyridine was used as the acetylation catalyst6, the alditol gave two peaks by g.1.c.‘. Similar results were obtained when sodium acetate was used as the catalyst*, and underacetylation was suggested*. We have reported’ the application to apiose of the method of Blakeney et al.“, which uses reduction with sodium borohydride in methyl sulphoxide and acetylation catalysed by IV-methylimidazole. The two peaks detected were assigned to apiitol tetraand penta-acetate and reflected the slow acetylation “g’* of the tertiary hydroxyl group at C-3. Complete acetylation requires elevated temperatures and extended times (90 min)‘. Kindel and Cheng13 obtained similar results, but reported that substantial proportions of 3-C-(acetoxymethyl)-1,2,4tri-O-acetyl-3-O-(methylthiomethyl)-D-glycero-tetritol were formed as a side product. We now present additional evidence that application of the method of Blakeney et al.” to apiose gives apiitol 1,2,3,4,4’-penta-acetate and 1,2,4,4’-tetra-acetate, and propose a method for quantification based on the latter derivative.

Lifting the lid on metatungstate. 1H and 183W NMR study of the six electron reduced anion [(H)2{WIV3(OH2)3}WVI9O34(OH)3]3–

The distribution of the eleven protons present in a six-electron reduced form of metatungstate, [(H)2{WIV3- (OH2)3}WVI9O34(OH)3]3–, in dry CD3CN is mapped by 1H and 183W NMR, allowing assessment of structural changes which accompany reduction.

Nitrogen-15 detection of broad amide protons in paramagnetic proteins

Nitrogen-15 detected NMR experiments allow identification of the broadened 1H resonances of amide hydrogens adjacent to paramagnetic centres in an electron transfer protein, the 2[Fe4S4] ferredoxin from Clostridium pasteurianum.

Assignments of 1H And 13C NMR of 6(9)-Methyl-Benzo[b]naphthyridines (5-Methyldiazaanthracenes)

Abstract A complete assignment of the 1H and 13C NMR spectra of four 6(9)-methylbenzo[b]naphthyridines in CDCl3 is presented. The proton signals have been assigned from (1H-1H) coupling patterns and by the comparisons of chemical shifts with those of related heterocycles. Complete 13C assignments have been made using proton detected one bond (13C-1H) 2D heteronuclear single quantum correlation, the INEPT technique, and chemical shift comparisons with related heterocycles. The proton detected long range (13C-1H) 2D heteronuclear multiple quantum correlation experiment leads to an unambiguous assignment of the two quaternary carbons in 6-methyl-benzo [b][1,5] naphthyridine.